1. Field of the Invention
This invention is in the field of electric arc furnace assemblies particularly of the type used for making steel and concerns itself with an improved shroud which fits around a portion of the electrode and protects the surface of the electrode from extensive exposure to corrosive gases and provides some lateral support when the electrode is displaced from its normally vertical position.
2. Description of the Prior Art
Electrodes for electric arc furnaces can be depleted by normal wear, by breakage, or by erosion caused by hot gases from the furnace being drawn along the tip of the electrode.
One of the major problems involving electrodes is that of breakage when the electrode comes into contact with the scrap steel in the furnace and is bent away from its normal vertical axis. Electric arc furnace electrodes are normally put together in sections. With a 28-inch diameter electrode, the full electrode may consist of three sections each about 110 inches long. The sections are joined together at their abutting surfaces typically by means of threaded nipples. When the electrode impacts against scrap steel in the bottom of the furnace, there is a substantial bending moment which frequently results in breakage of the electrode at the joint nearest the holder. The breakage of an electrode not only results in lost production time, but adds considerable expense to the steel making process.
There have been some disclosures in the prior art concerning devices for reducing the contact of the electrode surface with the corrosive gases of the furnace and in some cases providing a clamping pressure on the electrode under the roof of the furnace. For example, U.S. Pat. No. 1,363,815 to Saklatwalla et al. describes an electrode holder consisting of an outer metal casing which has a tapered opening or bore which seats a tapered metal ring or inner casing surrounding the electrode. A plurality of tapered metal wedges are arranged to be driven between the tapered interior of the ring and the cylindrical outer surface to secure the electrode and the ring together.
Sherman U.S. Pat. No. 2,979,550 describes an electrode seal having a stationary horizontal rim and a plurality of elongated cylindrical segments. The segments are pivotally supported from the rim on the inside so as to define a generally vertical aperture through which the electrode is received. The segments have internal passages for the circulation of water to serve as a coolant. Arrester blocks are provided between adjacent segments so as to form a gas-tight seal between the segments.
U.S. Pat. No. 2,982,804 to Reschke describes an electric arc furnace provided with a protective cylinder through which a gas is directed to protect the furnace against loss of heat, flame, and the presence of dirt around the cylinder.
U.S. Pat. No. 2,997,511 to Turner describes a water-cooled electrode head through which cooling water circulates, the cooling water directly engaging the copper body of the electrode head without an intervening cooling coil so that heat will be transferred effectively between the copper and the cooling water.
Krogsrud U.S. Pat. No. 4,434,496 provides a holder assembly for an electrode comprising a plurality of contact clamps which are pressed together toward the electrode by means of pressure-applying means and an external thrust member. The holder assembly is arranged to conduct current, coolant, and pressure agent to the contact clamps.
A shroud type cover is disclosed in U.S. Pat. No. 4,189,617 which deals with a liquid cooled electrode for electric arc furnaces. This patent suggests a cover which is electrically insulated from the electrode core, and in addition provides a device for producing a magnetic field in the lower portion of the cover. By means of the magnetic field, the electric arc is moved over the tip of the core so that an optimum position of the electrode tip can be defined by adjusting the axial displacement of the core.
European Pat. application No. 12573 of Montgomery describes an electrode including a water-cooled tubular column containing a number of interconnected graphite or carbon sections. The column surrounds one or more centrally extending bus bars and is insulated from them.
Mathgen et al. U.S. Pat. No. 4,457,002 is directed to a seal for an electrode passing through a furnace wall. The seal assembly is part of a closed chamber which is pressurized with an inert gas. A packing assembly compresses the seal ring radially against the electrode and includes split compression rings bearing axially on the seal ring.
Japanese Pat. No. 58-19892 provides an electrically conductive cylinder at least partially surrounding the part of the electrode extending into the furnace. The cylinder is water-cooled and delivers arc current to the tip of the electrode.
German Pat. No. 44401 to Wotschke employs a conductive shroud and ring in conjunction with a rotatable electrode for an arc furnace.